Over the last few decades, the electronics industry has undergone a revolution by the use of semiconductor technology to fabricate small, highly integrated electronic devices. The most common semiconductor technology presently used is silicon-based. A large variety of semiconductor devices have been manufactured having various applicability and numerous disciplines. One such silicon-based semiconductor device is a metal-oxide-semiconductor (MOS) transistor.
The principal elements of a typical MOS semiconductor device are illustrated in FIG. 1. The device generally includes a gate electrode 103, which acts as a conductor, to which an input signal is typically applied via a gate terminal (not shown). Heavily doped source/drain regions 105 are formed in a semiconductor substrate 101 and are respectively connected to source and drain terminals (not shown). A channel region 107 is formed in the semiconductor substrate 101 beneath the gate electrode 103 and separates the source/drain regions 105. The channel is typically lightly doped with a dopant type opposite to that of the source/drain regions 105. The gate electrode 103 is physically separated from the semiconductor substrate 101 by a gate insulating layer 109, typically an oxide layer such as SiO.sub.2. The insulating layer 109 is provided to prevent current from flowing between the gate electrode 103 and the source/drain regions 105 or channel region 109.
In operation, an output voltage is typically developed between the source and drain terminals. When an input voltage is applied to the gate electrode 103, a transverse electric field is set up in the channel region 107. By varying the transverse electric field, it is possible to modulate the conductance of the channel region 107 between the source region/drain regions 105. In this manner an electric field controls the current flow through the channel region 107. This type of device is commonly referred to as a MOS field-effect-transistors (MOSFET).
Semiconductor devices, like the one described above, are used in large numbers to construct most modern electronic devices. One important step in the fabrication of a MOS device is the formation of the gate electrodes. A typical MOS device includes a large number of gate electrodes. Conventional fabrication techniques provide a common gate electrode layer which is used to form the gate electrodes of the device. Typically, gate electrodes are formed by depositing a layer of polysilicon over a gate insulating layer, such as a silicon dioxide layer, patterning the polysilicon layer, and etching portions of the polysilicon layer to form a plurality of gate electrodes over the substrate. The above described conventional techniques for forming gate electrodes impose limitations on the fabrication of devices. In particular, the use of a common gate electrode layer to form each gate electrode can impose limitations on processing and inhibit optimization of transistor performance.